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Zozaya E.L.,Center Tecnologic Forestal Of Catalonia | Brotons L.,Center Tecnologic Forestal Of Catalonia | Brotons L.,Institute Catala d Ornitologia | Brotons L.,Center Recerca Ecologica i Aplicacions Forestais | And 5 more authors.
Ardeola | Year: 2012

Wildfires are certainly a key natural disturbance to terrestrial Mediterranean ecosystems. After an intense fire different types of habitats revert to relatively similar open habitats. This early successional stage has been shown to be used by many open-habitat bird species, which are able to colonise these new suitable habitats. By adopting a regional scale perspective, we assessed to what extent post-fire colonisation by open-habitat birds is constrained by the degree of isolation of burnt areas or the size of the burnt patch, and analysed the influence of the period elapsed since a fire on species colonisation. We focused on the Catalan population of the ortolan bunting Emberiza hortulana and estimated the amount of dispersal flux into a number of recently burnt areas as a measure of patch isolation, using regional data derived from atlas surveys and connectivity metrics based on graph theory. Our results show that species occurrence on recently burnt areas was primarily driven by the amount of dispersal flux, and to a lesser extent by the extent of the burnt area. Species occurrence also tended to increase with time since fire, suggesting that effective colonisation was partly driven by stochastic ecological and behavioural processes. We suggest that the prediction of species' responses to disturbances on large spatial scales should explicitly integrate not only species' responses to habitat changes but also information on dispersal constraints imposed by species' ecology.

Quesada J.,Institute Catala d Ornitologia | Guallar S.,Institute Catala d Ornitologia | Perez-Ruiz N.J.,Institute Catala d Ornitologia | Estrada J.,Institute Catala d Ornitologia | Herrando S.,Institute Catala d Ornitologia
Ardeola | Year: 2010

This study assesses the observer error of the Catalan Common Bird Survey (SOCC), a bird monitoring programme based on line transects. Specifically, it studies the error associated with assigning every detected bird to the correct distance band, and its influence in density estimates. Thirty SOCC participants were asked to allocate 20 objects detected along their line transect to 3 distance bands, while an evaluator measured the exact distances to the objects with a laser range-finder. Density estimates were derived both from exact and distance band data, the latter corrected or not corrected by the assessed error. Observer accuracy was high and precision low, although these varied with band boundaries. Estimates based on exact distances were significantly smaller than those based on bands. Band correction did not affect density estimates significantly. We suggest guidelines for detecting and reducing bias in observer error and for obtaining more reliable density estimates.

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